In recent years much interest has developed in solid state television cameras. These cameras use solid state sensors or imaging arrays, as they are sometimes termed, of photodiodes, charge coupled devices (CCD), bucket brigade devices (BBD) or other solid state, photoelectric transducers instead of the well-known vidicon tube. Each array is composed of a row and column matrix of photoelectric transducers to define a matrix array of photoelectric cells. Light from the object being imaged, impinges on the cells of the solid state imaging array, the cells being successively sampled by sampling pulses to produce electrical signals corresponding to the intensity of the light received by each of the array cells. In a color camera system, multiple solid state imaging arrays are used, with two or three arrays being the norm. In a two array system, it is known to produce two images of the object each containing light of only selected wave lengths using suitable prisms, dichroic mirrors, or filters, along with lens, mirrors and half mirrors. In this way, a first image may contain only the green light from the object and the second image its red and blue light. The green light is received by one of the two imaging arrays, while the red and blue light is received by the other imaging array. The cells of the arrays being CCD, BBD, photodiode or similar photoelectric devices, are sampled by sampling pulses to produce electrical signals proportional to the intensities of the green light and red/blue light received by the cells of the first and second array, respectively. These electrical signals are processed in conventional processing equipment to produce encoded signals representing the green, red and blue components of the object, for transmission to a compatible receiver where the encoded signals are decoded and the image of the object is reconstructed. It should be apparent and it is indeed well-known, that high resolution of the reconstructed image requires proper registration of corresponding cells of the two arrays.
It is also known to construct a solid state color television camera with three solid state imaging arrays, each consisting of a matrix of photoelectrical cells. As with the two array system, the three array system uses systems of prisms, filters, or dichroic mirrors along with suitable lens mirrors and half mirrors, to produce multiple images of an object, each image being of a selected color. For example, a first image might contain only the green components of the object, the second image only the red components, and the third image only the blue components. Light of the selected colors impinge a respective array where, in response to sampling pulses, the light is converted into electrical signals corresponding to the intensities of the green, red and blue light received by the cells of the first, second and third solid state imaging arrays, respectively. These electrical signals are encoded for transmission to a receiver where an image of the object is reconstructed.
Thus, the image of the object is broken down into a very large number of picture points or pixels and each point is divided into its primary color components. In solid state imaging, each cell of an array coincides with a picture point. When multiple arrays are provided for color transmission, corresponding cells in the different arrays define the color and intensity for each picture point. These corresponding cells must be maintained in a stringently defined positional relationship relative to each other to achieve optimum resolution.
This requirement of stringent alignment in color television cameras using multiple solid state imaging arrays has proven very difficult and often costly to satisfy. U.S. Pat. No. 3,975,760 which issued Aug. 17, 1976 to Yamanaka et al describes a multiple array solid state camera, each imaging array being composed of a matrix of CCDs, each CCD being considered a picture element. FIG. 5 of that patent illustrates a color camera apparatus in which the light image of an object is projected through a lens, half mirrors and mirrors to produce three images of the object. Each image passes through a different optical color filter positioned in front of a respective imaging array, the imaging arrays being formed on different chips. In this manner, each color image impinges on a different array, and the color intensity information at each picture element of the each array is read out and processed. Yamanaka et al recognized that the resultant video signal, which is the combination of the video signals produced by each array gave rise to base band and side band components which under certain circumstances gave rise to sampling error. This sampling error causes flicker in the picture reproduced from the resultant video signal. Yamanaka et al further found that this sampling error could be eliminated by very precisely locating one solid state array relative to another in the horizontal direction.
This task of precisely locating the arrays proved very formidable to Yamanaka et al. In U.S. Pat. No. 4,249,203 which issued Feb. 3, 1981 to Yamanaka, it is recognized that with a solid state array with several hundreds of picture elements (CCDs) in the horizontal direction it is extremely difficult to provide the necessary mechanical positioning of several arrays, each array being on a different chip. In Yamanaka, mechanical alignment of solid state arrays is abandoned for a complex and costly electronic alternative.
The requirement for accurate positioning of solid state imaging arrays exists not only in the limited situation of Yamanaka et al and Yamanaka where very precise horizontal displacements are needed to eliminate sampling error, but in general for it is necessary to position plural sensors in very specifically defined X, Y and angular positions relative to the image beam to correctly reconstitute the color image. If there is lateral, vertical or angular skew, the image on one image sensor will not superimpose exactly on the image of the others.
When the solid state imaging arrays of a color television camera are located in the manner illustrated in FIG. 2 of U.S. Pat. No. 4,415,924, which issued Nov. 15, 1983, to Kawabata, the positioning problem is very acute and can be practically solved only by the use of complex and expensive electronic solutions or through the use of specifically designed and expensive photoelectrical transducers such as those disclosed in the Kawabata patent.
It is known to modify the Kawabata positioning of multiple sensors and locate two sensors on a single printed circuit board. For this arrangment, reference is made to FIG. 5 of U.S. Pat. No. 4,369,459 to Iwasawa et al. In U.S. Pat. No. 4,264,921 to Pennington et al it is recognized that positioning plural arrays on a single chip or locating plural arrays on a single substrate simplify the task of aligning multiple sensors of a multiple sensor color facsimile apparatus.